The present invention generally relates to semiconductor processing, and in particular to an apparatus and method for removing small dust particles from substrates prior to assembly of Fine-pitch Ball Grid Array (FBGA) packages.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been, and continues to be, efforts toward scaling down device dimensions (e.g., to submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. These may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and surface geometry such as corners and edges of various features.
Assembly of devices with small feature size has necessitated the introduction of new assembly methodologies. One such methodology, which is now widely used, is Ball Grid Array (BGA) packaging. BGA packages are formed by placing an array of pads on a semiconductor substrate and solder balls on each pad.
A problem that arises, particularly when the BGA has a fine pitch, involves small dust particles interfering with the attachment of solder balls to pads. This problem is illustrated in FIG. 1, where a small dust particle 100 prevents solder ball 110 from properly contacting pad 120. As a consequence, ball 110 may be missing from the final array or insecurely attached to pad 120, resulting in defects.
High suction vacuums have been used to clean substrates. However, such vacuums are one or more of bulky, noisy, prone to mechanical breakdown, and expensive to maintain. Furthermore, high suction vacuums are not entirely effective in removing dust particles and create problems keeping the substrates in place.
One reason contaminants appear on substrates is that they are attracted by electrostatic charges that develop on the substrates during processing. High suction vacuum systems do not effectively mitigate development of these charges. Aside from attracting contaminants to the substrate surface, electrostatic charges create a risk electrostatic discharge, which can damage the semiconductor package.
There has been an unsatisfied need for better apparatus and methods that can be employed in FBGA packaging to effectively remove dust particles from substrates.
The present invention provides a method and system for blowing dust and other foreign particles off semiconductor substrate surfaces. The system may blow ionized air, which neutralizes electrostatic charges on the substrate surface thereby facilitating the release of particles from the substrate and reducing the risk of damage to semiconductor substrates from electrostatic discharge. The system also provides a vacuum for capturing dust particles blown off the surface, thus preventing the particles from contaminating clean room environments and redepositing on the cleaned substrate or other substrates.
One aspect of the present invention provides a cleaning system including a body, a blower outlet mechanically attached to the body, and a vacuum inlet mechanically attached to the body, wherein the shape of the body and the positioning of the blower outlet and vacuum inlet permit the blower outlet and vacuum inlet to be simultaneously placed in proximity to a surface to be cleaned whereby air blown from the blower outlet blows dust particles off the surface to be cleaned and blown particles are taken up through the vacuum inlet.
Another aspect of the invention provides a cleaning system including means for blowing ionized air onto a surface and means for capturing dust particles blown off the surface.
A further aspect of the invention provides a method of packaging semiconductor units including the steps of placing the units on a conveyor, conveying the units past a device that blows dust particles off the units with ionized air and captures blown dust particles with a vacuum, and subsequently conveying the units to an area where solder balls are attached to the units.